This invention relates to a process for dynamically partially gelling fluoroelastomers and to compositions comprising the partially gelled fluoroelastomers with ungelled fluoroelastomers.
Fluoroelastomer compositions are difficult to process efficiently. When uncured fluoroelastomers are extruded through a die opening to make a shaped article the fluoroelastomers have a strong tendency to swell after passing through the die orifice resulting in a shaped article which is much larger than the size of the die opening. Large die swell makes it very difficult to extrude articles with intricate cross-sections. The amount of pressure required to extrude fluoroelastomer compositions through a die orifice can be substantial, especially when a die with a small opening must be used due to the large amount of die swell that occurs. Furthermore, when uncured fluoroelastomers are extruded, frequently, the surface of the extruded article has a rough appearance unless special measures are taken, such as the addition of a wax-type extrusion aid and selection of extrusion equipment that can provide high extrudate temperatures of the order of 120.degree. C.
The present invention provides a process for making partially gelled fluoroelastomers dynamically, said fluoroelastomers having improved processing characteristics. The fluoroelastomers of this invention when extruded through a die orifice show a substantial reduction in die swell normally associated with fluoroelastomers. Further, the fluoroelastomers of the present invention when extruded have smoother surface characteristics than like fluoroelastomers.